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Chapter 2: Computer-System Structures

Chapter 2: Computer-System Structures. Computer System Operation I/O Structure Storage Structure Storage Hierarchy. Computer-System Architecture. Computer-System Operation. I/O devices and the CPU can execute concurrently. Each device controller is in charge of a particular device type.

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Chapter 2: Computer-System Structures

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  1. Chapter 2: Computer-System Structures • Computer System Operation • I/O Structure • Storage Structure • Storage Hierarchy Operating System Concepts

  2. Computer-System Architecture Operating System Concepts

  3. Computer-System Operation • I/O devices and the CPU can execute concurrently. • Each device controller is in charge of a particular device type. • Each device controller has a local buffer. • CPU moves data from/to main memory to/from local buffers • I/O is from the device to local buffer of controller. • Device controller informs CPU that it has finished its operation by causing an interrupt. Operating System Concepts

  4. Initialization • When computer is powered up, it needs to have an initial program that runs • Stored in ROM • Initializes device controllers, registers, memory contents, etc • Bootstrap program • Must be able to load the execute the kernel • Loads the kernel into memory Operating System Concepts

  5. Common Functions of Interrupts • Interrupt transfers control to the interrupt service routine generally, through the interrupt vector, which contains the addresses of all the service routines. • Interrupt architecture must save the address of the interrupted instruction. • Incoming interrupts are disabled while another interrupt is being processed to prevent a lost interrupt. • A trap is a software-generated interrupt caused either by an error or a user request. • An operating system is interrupt driven. Operating System Concepts

  6. Interrupt Handling • The operating system preserves the state of the CPU by storing registers and the program counter. • Determines which type of interrupt has occurred: • polling • vectored interrupt system • Separate segments of code determine what action should be taken for each type of interrupt Operating System Concepts

  7. Interrupt Time Line For a Single Process Doing Output Operating System Concepts

  8. I/O Structure • After I/O starts, control returns to user program only upon I/O completion. • Wait instruction idles the CPU until the next interrupt • Wait loop (contention for memory access). • At most one I/O request is outstanding at a time, no simultaneous I/O processing. • After I/O starts, control returns to user program without waiting for I/O completion. • System call – request to the operating system to allow user to wait for I/O completion. • Device-status table contains entry for each I/O device indicating its type, address, and state. • Operating system indexes into I/O device table to determine device status and to modify table entry to include interrupt. Operating System Concepts

  9. Two I/O Methods Synchronous Asynchronous Operating System Concepts

  10. Device-Status Table Operating System Concepts

  11. Direct Memory Access Structure • Used for high-speed I/O devices able to transmit information at close to memory speeds. • Device controller transfers blocks of data from buffer storage directly to main memory without CPU intervention. • Only one interrupt is generated per block, rather than the one interrupt per byte. Operating System Concepts

  12. Storage Structure • Main memory – only large storage media that the CPU can access directly. • Secondary storage – extension of main memory that provides large nonvolatile storage capacity. • Magnetic disks – rigid metal or glass platters covered with magnetic recording material • Disk surface is logically divided into tracks, which are subdivided into sectors. • The disk controller determines the logical interaction between the device and the computer. Operating System Concepts

  13. Moving-Head Disk Mechanism Operating System Concepts

  14. Storage Hierarchy • Storage systems organized in hierarchy. • Speed • Cost • Volatility • Caching – copying information into faster storage system; main memory can be viewed as a last cache for secondary storage. Operating System Concepts

  15. Storage-Device Hierarchy Operating System Concepts

  16. Caching • Use of high-speed memory to hold recently-accessed data. • Requires a cache management policy. • Caching introduces another level in storage hierarchy. This requires data that is simultaneously stored in more than one level to be consistent. Operating System Concepts

  17. Migration of A From Disk to Register Operating System Concepts

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